When the wheel of a motorized vehicle, such as an automobile, rotates at high speed, it is important that the wheel be properly balanced. At low speeds imbalance causes only minor difficulties, but with modern high speed vehicles and roads an unbalanced wheel presents major problems. In an unbalanced condition the wheel's center of mass does not coincide with its center of rotation, causing the wheel to vibrate and/or bounce on the pavement and leading to a number of undesirable effects. These effects include a shimmy in the steering mechanism of the vehicle, uneven wear on the tires and increased wear on breaking systems, front-end suspension systems and the like.
The common remedy in the case of passenger cars and other motorized vehicles for the conditions described above is to have the vehicle's wheels balanced. Various means have been utilized in the prior art for this purpose. One common wheel balancing technique is static balancing by the use of lead weights. In common practice such weights are typically clamped to the rim portion of the wheel. In an alternate arrangement, however, as described in U.S. Pat. No. 3,786,850 to Turocci, Jr., the weights may instead be attached to the outer surface of the tire.
While such weights may generally improve the wheel balance, they are incapable of producing optimal results since their position on the wheel is fixed and they thus tend to compensate for only a single imbalancing condition. Therefore, in the event that the condition changes due to tire wear or some other cause, the balancing effect provided by the weights is no longer effective. Further, installation of such weights typically requires the service of experienced mechanics and specialized equipment. Moreover, each time a new or repaired tire is installed on a wheel, the balancing operation must be repeated. Weights are frequently lost or misplaced when repairing or changing tires. Therefore, a large percentage of vehicles presently on the road are typically operated with unbalanced wheels, and are therefore prone to many of the problems described above.
There has thus been a continuing interest, among those working this field, in the development of balancing means adapted to be permanently mounted upon a vehicle wheel. It has been further deemed desirable that such means be capable of continuous operation as the wheel rotates to provide a dynamic counterbalancing effect to offset any static imbalance existing or created in the Wheel and/or tire assembly. In this regard, various dynamic balancing mechanisms or devices have been developed in the prior art which are adapted for installation upon the wheel of a motor vehicle. Most such devices, as described below, incorporate in some manner a quantity of weighted elements and/or a damping fluid which is distributed about the rotational axis of the wheel, as the wheel rotates, to a position diametrically opposite to the mass tending to cause imbalance to the wheel and/or the tire to provide a partial counterbalancing effect.
As described, e.g., in U.S. Pat. Nos. 3,164,413 and 3,316,021 to Salathiel; 3,346,303 to Wesley; 3,376,075 to Mitchell and 5,253,928 to Patti, in one version of such prior art dynamic balancing devices, the weights and/or fluid are contained within a hollow annular hoop member which is secured in some manner, e.g., with the use of fasteners, to the outer surface of the hub portion of the wheel.
U.S. Pat. Nos. 3,164,413 and 3,316,021 to Salathiel describe a hollow annular hoop containing a plurality of spherical weights and a damping fluid. The annular hoop is made of a plastic material. In use, the hoop is attached to a rotating wheel and the weights are free to move within the hoop. The damping fluid reduces noise as well as restricts the free movement of the weights. The weights are urged toward the point in the hoop which offsets the imbalance of the wheel.
The apparatus described in the Salathiel patents, however, has the disadvantage of using a deformable material, i.e., a plastic, for the annular hoop. Under conditions of rotation at high speed the hoop can bulge where it is free to move and this loss of concentricity causes an imbalance to the device. Loss of concentricity of the hoop can also prevent free movement of the weights.
U.S. Pat. No. 3,346,303 to Wesley describes a hollow annular hoop containing a plurality of spherical weights and a measured amount of damping fluid. The hoop has an apex at its outer perimeter and is adapted with the outer apex to provide reduced areas of contact between the spherical weights and the hoop when the hoop is rotated. The hoop is constructed of a metal formed or welded into the proper shape or configuration and is attached to the wheel of the vehicle by use of a mounting fixture which has several precut lug nut holes adapted to fit the wheel.
U.S. Pat. No. 3,376,075 to Mitchell describes a dynamic wheel balancing device which includes a hollow annular hoop with a plurality of spherical weights and a damping fluid. The hoop is attached to a mounting fixture which is adapted to fit a variety of wheel and lug nut configurations. The annular hoop is constructed by attaching a U-shaped channel onto a plate in a fluid tight manner.
U.S. Pat. No. 5,253,928 to Patti describes a method for attaching a dynamic wheel balancer to a vehicle wheel. The balancer is a hollow annular tube containing metal balls and a damping fluid, e.g., an oil. The wheel balancer is concentrically mounted against the wheel, preferably against the outside of the tire rim. The balancer may be installed by either placing it within a recess formed in a wheel cover and attaching the wheel cover to the wheel, or alternately, by placing the balancer against the wheel and holding it in place with, e.g., adhesive tape while the wheel cover is attached.
One drawback to the use of balancing means including spherical weights as described above for the dynamic stabilization of a tire and/or wheel assembly is that the surfaces of the balancing spheres tend to suffer from some limited degree of corrosion over time. The resultant corroded surfaces tend to become wetted and sticky by exposure to the damping fluid which is employed. The balancing spheres thus tend to bunch up and stick together. They stick together with increasing frequency and tenacity as the balancing weights are reduced in size, thus exposing a larger wetted surface to the other balancing weights. Under such conditions, therefore, groups of such weights tend to become wedged when attempting to pass one another or in passing a weight stuck to the inner surface of the annular tube or hoop.
Another significant disadvantage to the use of the dynamic balancing means described above is that such means require the vehicle owner to "add on" a heavy awkward ring structure to the vehicle wheel. The use of such a device not only requires significant time and effort for its installation, but also adds appreciably to the weight of a vehicle wheel so equipped.
Thus, in a further effort to at least partly overcome the disadvantages discussed above, there has been developed dynamic stabilizing means installed upon an inner surface of a motor vehicle wheel between the flanges comprising the wheel rim. One major drawback of such means, however, is that they typically protrude upwardly into the air cavity of the tire, thus filling in the drop center of the rim, thereby interfering with the ability to mount and dismount the tire from or onto the rim. In an effort to overcome this problem, internal dynamic balancing devices have been developed which are adapted to be recessed below the drop center of the wheel. An example of such an arrangement is illustrated in U.S. Pat. No. 2,737,420 to Wilborn.
The Wilborn patent describes a means for dynamic balancing of motor vehicle wheels embodying a wheel comprising a rim portion having an annular recess and a band positioned upon the rim providing a closure for the recess so as to form an enclosed channel running around a central portion of the wheel. This channel may be provided with a plurality of globular balancing elements and a quantity of damping fluid which circulates around the circumference of the wheel during rotation to produce a dynamic balancing effect while the wheel is in motion.
The arrangement described in Wilborn, however, suffers from a significant drawback in that the dynamic balancing forces thus provided are brought to bear only within an inner central annular portion of the wheel mass. Thus there is only limited balancing of vector forces along the X (side to side) and Y (up and down) planes and no balancing at all of the vector forces along the Z (yaw-type movement) plane. Moreover, in addition no balancing effect is obtained with the use of means such as those described in Wilborn at the outer fringes of the wheel where it is needed most, i.e., at the flange portions of the wheel rim, which are the most likely areas to require balancing due to the unbalancing effects of tire irregularities, the presence of valve stems, dents due to impact with curbs, potholes, etc. and the attachment of road debris.